Vacuum Tube Wah

[R.G.]

This isn't new, but I find that people tend to miss or forget the things at GEO, and *I* was reminded of it by some email.

There's a vacuum tube based wah circuit at GEO,

http://geofex.com/Article_Folders/tube-wah/tube-wah.htm

It's a straightforward tube implementation of the Vox inductor wah, and I'm now had over a dozen reports that it works...great...

Some of the versions used the MOSFET, some used another 12AX7 for the cathode follower, and they both seem to be good. Reports are that it's quite sensitive to the initial setting of the wah pot on the rack, and that it gives a very vocal Vox wah sound.

If you want to mess with some tube stuff, this might be a good place to start. The power supply is set up to work with a 12Vac wall wart and an onboard 120:12Vac transformer for high voltage. All the normal cautions about tubes apply: high voltage is dangerouse, so **don't** try this unless you can do it safely.

[puretube]

TUBE-WAH(R)

is a registered trademark of Anthonie Th. Barmentloo...

[petemoore]

Looks like elegance with HV tubes for the Wah Coniaseur.
 Plenty of tested mods for the inductor wah...
 A Very tempting build, but with substantial tasks.
 Shaping and working the metal also can be hazardous ...
 I dont' know of any treadle/shells that would house a tube'n related circuit...
Mount the 'side plate', which will be the 'floor' for the 'new room addition' [perhaps an L shape sheet, adding wood struts for strength and feet, so the tube circuit is mounted and resides next to the wah shell, top right, or in front of the toe], using the VOX shell's bottom plate screws, and mount the Tube 'n circuit to the shielded box...run the wires to jacks, BP switch and inductor...

[casey]

you can find a schem. on my site of a svetlana tube wah by e. barbour....

http://photobucket.com/albums/v324/caseyseffectpage/Wahs/?action=view¤t=svetlanafuzzwah.jpg

cool stuff.

[R.G.]

TUBE-WAH(R) is a registered trademark of Anthonie Th. Barmentloo...

Yes, I know that. That's why I was careful to refer to "vacuum tube wah" and "vacuum tube based wah". I would not dare to infringe on the rights of someone who has had the foresight to stake a claim to a set of words.

As I understand it, the circuit of the "TUBE-WAH(R)" is a vacuum tube implementation of the multiple feedback bandpass filter with tubes instead of opamps. That's one reason I pointed out the further difference that this one is an implementation of the Vox inductor based circuit, which I and some people prefer the tone of. Matter of taste, really.

Of course, owning the rights to the use of the words "TUBE-WAH(R)" lets the owner put anything they like in there, since the words don't imply anything in particular about the circuit, so that could have been, or in the future may be changed to the Vox style circuit. I really don't know.

you can find a schem. on my site of a svetlana tube wah by e. barbour....

And Eric's version of a vacuum tube wah uses a multi-henry iron cored inductor and a - big - AM radio style moving plate variable cap to sweep the wah resonance.  Sourcing that variable cap is a modest-to-major pain, depending on how many old tube style AM radios you have lying about.

[Paul Marossy]

Hmm... I wonder if it's possible to fit that vacuum tube wah circuit in a CryBaby shell? You could lay the tube down flat in there. I'm just not sure about the internal transformer...

EDIT: You only need 100mA for that internal transformer?! Is that because the wall wart is 500mA?

EDIT #2: Nevermind, I looked closer at the text.  :oops:

[puretube]

the full story of the TUBE-WAH(R) will be written down one fine day in its historical contest -
- including how it evolved into the invention of the TUBE-TRON(R) in 1971 - and who really played the first envelope-followah the first time...

(the full story is known by the persons concerned   )

[Gladmarr]

Hey, I actually built the e. barbour tube-type wah a few years ago.  It hums like a Mother!  I think I actually built a nasty ground loop into it.  I've been meaning to revisit that someday.  For now it's living in the closet of freaks and mutants.

http://www.angelfire.com/indie/gladmarr/index.html

The pic's not all that good.  But it's there alright.....

[puretube]

Hmm... I wonder if it's possible to fit that vacuum tube wah circuit in a CryBaby shell? You could lay the tube down flat in there. I'm just not sure about the internal transformer...

sure:


http://www.pure-tube-technology.de/TW527.jpg
http://www.pure-tube-technology.de/TW528.jpg
http://www.pure-tube-technology.de/TW533.jpg
http://www.pure-tube-technology.de/TW534.jpg

(well, it`s not a CB-shell, but an exact clone by Schaller-shell...)

[Paul Marossy]

Thanks for the pics! Interesting. I bet it could be done PTP with some careful thought.  

The only thing that I don't see in those pictures is an interanally mounted transformer...  

[puretube]

there`s a tiny empty spot in the lower right end of the pedal in this pic:
http://www.pure-tube-technology.de/TW528.jpg...

that`s where the 80kHz 12V to 250V HF-transformer used to sit before it went into the pedal on top of this thread...
(incidentally the same type and size core, as the classic wah inductors);

(it was the DC-powered version from 1996, with built in HF DC/DC converter, before new radiation requirements were introduced in europe).

That`s why you see 2 power-semiconductors on the bottom plate:
a voltage regulator, and a HF power transistor...

BTW: note the yellow rubbers shock-proof mounted tube-socket!
(http://www.pure-tube-technology.de/TW534.jpg)

PS: the mentioned TUBE-TRON(R)`s workalike is currently better known as Electro-Harmonix`s "Tube Zipper".

[Paul Marossy]

I was wondering what those semi's were on the bottom plate for.  :wink:

[Paul Perry (Frostwave)]

Anyone know who to credit for this tube wah circuit?
http://www.muzickicentar.co.yu/sheme/effects/wahsweel/WahWahTube12AX7.jpg

[sir_modulus]

Hmm...Thanks puretube. You've given me a good idea! I can now get power transformers without the filament winding, and just use voltage regs....They'd be cleaner!

Cheers,

Nish

[puretube]

that`s probably already been said or mentioned in all of those "toroidal" threads :?:

[sir_modulus]

Sorry I don't pay too much attention  

I remember a time when that GEO article had a variable capacitor rather than a Wah pot, so I never had a second look. I do agree though...some new peeps here should have a nice long gander at GEO, I've read a lot of stuff on there, and there is very very very little "useless information". (Good job RG, on a site well done....I have a question for you though....can a purchase on of 'em PCB layout books from you?)

Cheers,

Nish

[R.G.]

So, pure, those look really cool. How about showing us the schematic for that, as I did for mine?

Thanks for the pics! Interesting. I bet it could be done PTP with some careful thought.

Easier with a PCB and an aluminum L-bracket for the tube socket.

Anyone know who to credit for this tube wah circuit?

That ... was... a trademark infringement, right pure?
I believe that's the one I pointed out as a multiple bandpass filter unit. Might as well use opamps - the tube-iness won't come through that much. Feedback hides it, and you have to have the feedback to make the filter work. I don't know who to credit, though.

Hmm...Thanks puretube. You've given me a good idea! I can now get power transformers without the filament winding, and just use voltage regs....They'd be cleaner!

And hotter. If you run the tubes from 100Vdc ore more (highly recommended), then you linearly regulate, you have to provide 150ma to the filaments if they're in series, and that's (100V-12V)*150ma = 13.2watts of power to get rid of, and you'll need to do something to get the raw 100V down to the 40V that a three terminal reg can live with.

I remember a time when that GEO article had a variable capacitor rather than a Wah pot, so I never had a second look.

To the best of my recollection, I never posted a variable cap version. Am I getting senile?

can a purchase on of 'em PCB layout books from you?)

soon... I'm waiting on some commercially bound copies.

[sir_modulus]

Whoops...sorry, I thought that was Geofex...I remember it was a big PDF article, and I kinda linked it in my mind to Geofex.....

good good! I'm looking forward to buying a copy of your book!

Cheers,

Nish

[R.G.]

I think it must have been eric barbour's article on the svetlana one.

[Marcos - Munky]

Just a dumb question: what is the difference in the sound between a inductor wah and a tube wah? I don't know the advantages of a tube wah, maybe it's because I played only in inductor wahs until now .